Recovery crews were still searching for wreckage on Friday of a sightseeing helicopter that appeared to break apart over the Hudson River a day earlier before slamming into the water, killing all six people on board.

Among the pieces that have not been recovered as of Friday afternoon was the main rotor, according to Jennifer Homendy, the chair of the National Transportation Safety Board. The part was shown flying off the plunging craft in videos captured by witnesses.

Ms. Homendy cautioned, however, that the investigation was just getting underway, and would not speculate on a cause of the crash.

“Everything is on the table — we don’t rule anything out,” she said at a news conference with officials from Jersey City, near the site of the crash, on Friday afternoon. No timetable was offered for the investigation.

A team of 17 agents were on site to begin the painstaking process of reviewing the condition of the aircraft, a Bell 206L-4 helicopter, which was still missing the main and tail rotors, the main transmission and hunks of its structure. The aircraft departed a heliport in Lower Manhattan at about 2:50 p.m. on Thursday and crashed at approximately 3:15 p.m., Ms. Homendy said.